The Muscular System Mrs. Hartley Anatomy and Physiology

All 500+ muscles of the body share 3 major functions: Movement: integration of bones, joints, nerves, and musclesMovement: integration of bones, joints, nerves, and muscles Support: hold in upright position/form skeletal frameSupport: hold in upright position/form skeletal frame Heat Production: heat is a by-product of movement to help maintain normal body tempHeat Production: heat is a by-product of movement to help maintain normal body temp

All Muscles Share 4 Basic Properties Contractility: ability of a cell to shorten in lengthContractility: ability of a cell to shorten in length Excitability: ability to receive and respond to a stimulusExcitability: ability to receive and respond to a stimulus Extensibility: ability to increase in lengthExtensibility: ability to increase in length Elasticity: ability of a cell to return to its resting form after contractionElasticity: ability of a cell to return to its resting form after contraction

Note the organization of the muscle: contractile protein filaments are bundled into myofibrils; bundles of myofibrils are contained in each individual muscle fibre (cell); muscle fibres are bundled to form fascicles and the fascicles are bundled to form the muscle organ.Note the organization of the muscle: contractile protein filaments are bundled into myofibrils; bundles of myofibrils are contained in each individual muscle fibre (cell); muscle fibres are bundled to form fascicles and the fascicles are bundled to form the muscle organ.

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Physiology of Muscle Contraction Fiber is at restFiber is at rest Stimulus occurs: Ach, action potential, increase permeability to CaStimulus occurs: Ach, action potential, increase permeability to Ca Contraction: Sliding filaments of actin and myosin with energy from ATP, shortening of sarcomeres in myofibril causes muscle contractionContraction: Sliding filaments of actin and myosin with energy from ATP, shortening of sarcomeres in myofibril causes muscle contraction Return to Rest: ATP regenerated by mitochondriaReturn to Rest: ATP regenerated by mitochondria

Energy for Contraction ATP: Used up in a matter of secondsATP: Used up in a matter of seconds Creatine Phosphate: stored for long periods of time; 4-6 times more abundant than ATPCreatine Phosphate: stored for long periods of time; 4-6 times more abundant than ATP Glycogen: without these stores, our muscles would only sustain activity for less than 15 seconds; yields ATP when broken downGlycogen: without these stores, our muscles would only sustain activity for less than 15 seconds; yields ATP when broken down Fat: utilized last; prolonged and strenuous exerciseFat: utilized last; prolonged and strenuous exercise

Oxygen Debt Required in synthesis of ATPRequired in synthesis of ATP Levels become depleted after several minutes of exerciseLevels become depleted after several minutes of exercise Lactic Acid accumulates producing soreness you experience after exerciseLactic Acid accumulates producing soreness you experience after exercise Rapid and deep breathing compensate for this debt by bringing in oxygenRapid and deep breathing compensate for this debt by bringing in oxygen

Exercise Benefits Highly trained athletes produce only ½ as much lactic acid Achieve greater levels of activity before oxygen debt begins

Muscle Fatigue Muscles exercised strenuously for a prolonged period of time Inability of muscle to contract in a normal manner Accumulation of lactic acid, decrease in Ph, cramps

What Causes a Cramp? Commonly called “charley horse”Commonly called “charley horse” Muscle contracts spasmodically without relaxingMuscle contracts spasmodically without relaxing Insufficient amount of ATP to return calcium ions to their proper place resulting in lack of relaxationInsufficient amount of ATP to return calcium ions to their proper place resulting in lack of relaxation

3 Types of Muscle Skeletal MuscleSkeletal Muscle Smooth MuscleSmooth Muscle Cardiac MuscleCardiac Muscle

Skeletal Muscle Primary component of body’s musclesPrimary component of body’s muscles High strength due to high organization and combined contractionsHigh strength due to high organization and combined contractions VoluntaryVoluntary

Cardiac Muscle Rectangular in shape with a single nucleus Intercalated discs facilitate stimulus conduction b/w cells to function as a unit Visible striations Forceful but not as much as skeletal muscle No oxygen debt or muscle fatigue Needs no external stimulus

Smooth Muscle Small and spindle-shaped cells with single nucleus Different protein distribution than skeletal: no troponin, fewer actin Contract slowly and with less force however can sustain a contraction longer No oxygen debt Usually needs an external stimulus by nerves or hormones